Magnesium oxide pellets and process of



July 30, 1963 c. D. VAUGHAN, JR.. ETAL 3,099,533

MAGNESIUM OXIDE PELLETS AND PROCESS OF PRODUCING THE SAME FOR BURNING Filed Dec. 6, 1960 d'ALC/MFD M90 FEEDER ATTORNEY United States Patent 3,099,533 MAGNESIUM OXIDE PELLETS AND PROCESS OF PRODUCING Tim SAME FOR BURNING Chester D. Vaughan, Ira, and Richard H. Vetter, Freeport, Tern, assignors to E. .i. Lavino and Company,

Philadelphia, Pa, a corporation of Delaware Filed Dec. 6, 1960, Ser. No. 74,021

3 Claims. (Cl. 23201) This invention relates to the compacting of powdered magnesium oxide into discrete bodies for burning.

In connection with the forming or compacting of fine magnesium oxide powder into small bodies or briquettes, the conventional procedure is to introduce the magnesia powder between opposing compressing rolls having symmetrical recesses or depressions therein which are brought together to compact the powder therein and therebetween and in following this procedure the powder is formed into bodies or pellets shaped to desired form, which may be spherical or almond shape.

Because of the fact that the magnesia, from whatever source it may be obtained, is in the form of a dry powder when subjected to the briquetting operation, difiiculty is experienced in causing the powder to agglomerate. This leads to :a number of troublesome problems, among which are that the two symmetrical halves of the shaped body or pellet fail to adhere together properly in the press and therefore, upon the discharge of the body, the two halves thereof separate or split apart.

In addition to the fact that the halves of the pellet tend to split, these split halves are weak and friable and tend to break up in the handling, particularly at the time of their discharge from the press.

It is a particular object of the present invention to provide .a novel process whereby the present problems associated with the production of magnesium oxide pellets are eifectively overcome.

Another object of the invention is to provide a novel process or procedure whereby the magnesium oxide powder will be caused to firmly agglomerate to formthe desired pellets when the powder is compressed between the compression rolls of the briquette press so that the pellets will be in a form suitable for firing in shaft kilns.

Still another object of the invention is to provide a new and novel process for producing magnesium oxide pellets in the desired shape or form by combining with the powder prior to the compression of the same in the briquetting press, a suitable fibrous bonding material which will cause the powder to properly agglomerate and accordingly provide a pellet which will maintain its shape or form upon being discharged from the pressing or briquetting machine.

A further object of the invention is to provide a process for the production of magnesium oxide pellets of a hard dense character designed primarily for the production of a refractory brick mix, which pellets can be crushed and selectively sized to provide the proper sizes for the brick mix.

It is another object of the invention to provide magnesium oxide pellets having combined therewith an organic fibrous material which, in addition to functioning as a means for causing the dry magnesia powder to maintain its compacted form in the pellet, can be substantially or entirely eliminated during the calcining of the pellets.

Other objects will become apparent when considered in connection with the specification and accompanying drawings, wherein:

FIG. 1 illustrates schematically a preferred and effecform and hardness or compactness.

selected organic fiber to pounds of calcine.

3,099,533 Patented July 30, 1963 "ice FIG. 2 illustrates a pellet formed in accordance with the hereinafter described process and shown prior to firing, such pellet being illustrated in the form or shape of an almond and which pellet is shown as viewed from one convex side or face.

'FIG. 3 is a side or edge view of the pellet.

1816. 4 is a sectional view taken on the line 44 of F1 2.

FIG. 5 is a view of a pellet initially having the same size as that shown in FIG. 2 but showing the darkened condition of the pellet after being fired in the shaft kiln and also illustrating the approximate extent of shrinkage of the same, from the initial size, which is designated by the broken outline.

In accordance with the present invention, magnesium oxide initially is given a light calcining by subjecting the same to a temperature of from 1300 to 1500 F.

The magnesium for use in carrying out the process of the present invention may be obtained from any suitable source, such as from sea water, magnesite rock or brine wells. When, for example, the source is sea water the magnesium is produced initially in the form of a slurry of magnesium hydroxide which, through filtering, has a substantial amount of the water removed. There is thus obtained a filter cake of the magnesium hydroxide and in .the magnesium oxide, generally referred to as calcine.

The calcine thus obtained is then combined with a suitable organic material, preferably a material of fibrous character, and this mixture of the magnesia powder, or calcine, and organic material or binder is then run into or through a suitable and conventional form of briquette New One form of press suitable for forming the briquettes in the shape desired is that known as the Komarek-Greaves briquettepress. This particular make of press may be obtained with dies fior producing bodies of different forms and while a briquette of almond shape or form has been selected for illustration and description another desirable and possibly more nearly ideal form.- of briquette for use in a shaft kiln is a-sphere. Accordingly, it will be understood that even through the form of the briquette has been illustrated as that of an almond the invention is not limited to this form orto any specific form for the magnesium oxide briquette since the invention resides in the process of producing the briquette in the proper or ideal condition for subsequent handling and use in the making of ref-ractory brick.

A number of different organic materials; may he employed, such, for example, as cotton thread, cotton waste, shredded newspaper, excelsior and cotton or rayon flock.

, Rayon or cotton flock are the preferred substances for use.

' within certain limits, it has been found that the best results are obtained by using approximately 5 ounces of the This fibrous material is metered onto the calcined magnesia as the latter is carried from the source of supply to the briquette press and means is provided whereby, during the period of transportation to the press, the powder and the fiber are thoroughly mixed together.

It has also been found that the best results are obtained by the use of a fiber of small cross sectional area. Such fibers produce a better agglomeration of the powder than larger fibers which tend to produce a spongy briquette.

Another condition required in connection with the production of pellets or briquettes of the proper degree of hardness or consistency is that the fiber must be physically constituted so that it can be properly metered into the calcine by an appropriate means which will separate the fibers one from another to thereby allow the mixing and dissemination of the same through the calcine.

In stating that the fibers must be physically constituted so that they can be properly metered this means that the fibers must be of such a nature as to readily separate from one another. For example, the fibers contained in cotton batting would be suitable or even ideal for use except that they have a tendency to cling to one another because of their length and because of being intertwined. Accordingly, it would be an extremely diflicult job to separate the fibers of the cotton batting, fiber by fiber, and attempt to disseminate them through powdered calcine. However, these same fibers when cut into short lengths do not exhibit the tendency to cling and they will then separate one from another so that the metering of the fibers can be effectively accomplished.

In connection with the separation of the selected fibers and the reduction of the same to desired lengths it has been found that the most desirable length is between from 0.05 to 0.075 millimeter and it has also been found that the most desirable fibers are those having a diameter somewhere in the neighborhood of 0.0015 millimeter. It has been found that large coarser fibers do not have as effective a binding capability although, while the ideal diameter and length for the fibers has been set forth, it is possible to use coarser fibers with fairly good results and therefore it is to be understood that in setting forth the above figures there is no intention to so specifically limit the claimed invention.

Rayon fiber is also a good fiber for use and have less tendency size for size to cling to one another than cotton fiber. Accordingly, either of these fibers may be found most desirable from the standpoint of economics.

It is also desirable that the selected fiber be of such composition that when the briquette is exposed to a temperature of 3000 F. or more, the fiber will burn out of the briquette. This, of course, is a condition which limits the fibers to those of organic nature.

Referring now to the drawing, the numeral designates a suitable type of receptacle or surge bin from which the calcined magnesium oxide is discharged by means of a feeder 12 onto a conveyor which is generally designated 14. This conveyor 14 conducts the calcined magnesium oxide pasta fiber storage bin 16 from which the fiber is fed and metered by a feeder 18 onto the calcined magnesia carried by the conveyor.

Wln'le any suitable means may be provided for feeding and metering the fiber at the position or stage designated 18, onto the conveyor 14 use has been made of, and preference is had for, a vibratory type of feeder having a variable control of rate of flow such as that feeder which is obtainable on the market under the name of Syn-tron. This feeding device operates on the vibratory principle and is controlled by a rheostat for regulating the rate of feed. Such feeder is located beneath the outlet of the fiber storage bin.

Beyond the feeder 18 from which the fiber is trans ferred from the fiber storage bin onto the conveyor, the two materials, namely the magnesium oxide powder and the fiber, are agitated and mixed as they move along, by the action of the conveyor itself.

A preferred type of conveyor is that known as the Link Belt Coilmount oscillating conveyor. Such conveyor is of a trough type and is resiliently mounted and is mechanically actuated in a manner to effect the movement or advancement of the materials in the desired direction. This agitation of the conveyor will effect the mixing of the materials but if desired the conveyor may be equipped with fixed vanes in the bottom thereof which will cause the material to have additional movement and therefore effect a more thorough mixing of the same. This mixing of the 4 materials will occur in the portion of the conveyor designated 20.

The numeral 22 generally designates a surge bininto which the mixed magnesium oxide and fiber are discharged and which bin feeds the mixture to the Koma-rek Greaves briquette press here schematically illustrated and generally designated 24.

The numeral 26 designates a suitable link belt bucket elevator which receives the calcine and fiber mixture at the location designated 28 and carries it up and discharges it into the surge bin as indicated.

The formed pellets of magnesium oxide and fiber are discharged from the press onto the oscillating conveyor which is generally designated 30. This conveyor includes in a portion thereof a separator means or grizzly generally designated 30a.

The briquetting press embodies a pair of die rolls positioned in peripheral contact and such die rolls rotate toward each other and have matching depressions therein which come together in accurate alignment as the rolls turn so as to form the die chamber in which the material is compressed in the form of the briquette. The calcine and fiber mixture is fed down from the surge bin between the rolls of the press. As the rolls turn or rotate the briquettes are formed in the die portions thereof and then as the trolls separate the formed briquette is discharged, the two die portions of the trolls separating and pulling away from the surfaces of the briquette so that the biiquette is freed to drop down and pass onto the conveyor 30. Ideally, as the two rolls separate or pull apart, the formed briquette should free itself and drop down as a whole briquette. However, there is a tendency for the two matched dies to cling to the surfaces of the b-riquette and as the rolls separate there is a tendency for the die halves to pull the briquette apart. is a condition where briquettes are tormed without bonding material but the use of fibers in accordance with the present invention forms a good bond which prevents such separation.

The discharge from the briquette press is, quite naturally, not all acceptable product. A portion of the calcine going into the press is carried through the press via the lands between the dies or the die halve-s in the rolls and is discharged in approximately the same physical condition in which it entered the press. Obviously, therefore, the function of the grizzly 300 which forms a unit in the conveyor 30 which carries the briquettes from the press, is to screen and separate the chips and fines from the whole briquettes. The grizzly component mounted in or forming a unit of the conveyor is a screening device embodying a set of spaced bars to effect the desired size separation.

The chips and fines are discharged from the grizzly onto a conveyor 31 and carried back to the point 28 where the bucket elevator receives the calcine and fiber from the conveyor 20, to be returned by the bucket conveyor to the surge bin for recycling through the briquette press. The separated briquettes are carried by the section 30b of the conveyor 30 to the conveyor '32 to be carried thereby to a suitable receiver or to the shaft kiln to be subjected to the filing temperature.

The molded briquctte as it leaves the press is in a hard or firm compact mass. This condition results from the combining with the powdered magnesium oxide of the selected fibrous material and while the body of the pellet shows an encircling roughened belt around the length thereof as at 33 between the smooth compact halves 34, the bonding of the fibers with the powder is such as to effectively prevent fracture of the pellet or separation of the same around the belt area 33, as has been the difiiculty associated with the tormation of the pellets heretofore when no bonding material has been used.

Following the formation of the pellets or briquettes the same are introduced into a suitable kiln and subjected to a firing temperature of above 3,000 F. At this temperature the fibrous material in the pellet is burned out and a certain amount of shrinkage in the size of the pellet occurs and in addition the pellet which initially is of a creamy color or complexion assumes a darker or light brown complexion as is shown in FIG. 5 where the burned pellet is illustrated and which figure shows the same as considemably darker than is illustrated in FIGS. 2 and 3.

While the formed pellet clearly shows two distinct smooth surfaced halves with a rough narrow belt between them as indicated at 33 in FIGS. 3 and 4, the material is compacted to such a degree that separation of the halves does not occur. Heretofore the pellets, after being formed and when no bonding material was incorporated with the calcine, would easily split or fracture through the belt line and thus split into two halves which, as hereinbeforc stated, were easily broken or very friable.

As previously stated, FIG. 5 illustrates in association with a broken line depicting the initial size of the pellet, the extent of shrinkage which occurs after burning and in this figure the broken line which depicts the initial contour of the pellet is designated 35, while the burned pellet is designated 34a, and it will be seen that there is a considerable shrinkage between the burned pellet and the initial size of the pellet, the extent of the shrinkage being shown by the space 36 between the broken line 35 and the burned pellet 34m.

The briquettes when placed in the shaft kiln are fired to a very high temperature. The firing of the briquetted calcine to a high temperature has the efiect of recrystallizing the magnesium oxide into a hard, dense pellet which can then be crushed and selectively sized to provide the proper sizes for a refractory brick mix. There is practically no difference between the green briquettes and the fired product or periclase, both being still magnesium oxide. The change which occurs as a result of the firing at high temperatures is a physical one. This is seen as a conversion of the compacted material to a crystallized state which entails considerable shrinkage.

In connection with the formation of the briquettes ideally as spheres or as almond shaped bodies it is extremely important to the success of the shaft kiln to feed it with briquettes which are strong and whole and which exhibit the least tendency during movement to deteriorate in any way. Because of this it is highly important that the briquettes be of sufficient hardness or strength to minimize to the greatest possible extent the splitting thereof and also the elimination of any fine material which might be introduced into the kiln. The largest single detriment to the success of a high temperature vertical shaft kiln is fine material and difficulties heretofore encountered in the operation of the shaft kiln can be related back directly to fine material entering the kiln as the result of the deterioration of the briquettcd feed.

Briquettes formed according to the present invention are extremely resistant to abrasion, impact splitting and attrition. In other words, such briquettes can be conveyed, tumbled or handled and will produce only a minimum of splitting or generation of chips or fines.

As this invention may be embodied in several :Eonms without departing from the spirit or essential characteristics thereof, the present embodiment is therefore illustrative and not restrictive, since the scope of the invention is defined in the appended claims, and all changes that fall within the metes and bounds of the claims, or that form their functional as well as conjointly cooperative equivalents, are therefore intended to be embraced by those claims.

We claim:

1. A compact dry magnesium oxide pellet containing as a binder approximately 7 percent of relatively fine cellulosic fibers of a length of from about 0.05 to 0.075 millimeter and of a diameter of the order of about 0.0015 millimeter and having a sufficient hardness to resist cracking and decrepitation on introduction into and passage through a shaft kiln.

2. A dry process of forming pellets of magnesium oxide capable of free handling without disintegration, which consists of selecting fibers of readily combustible organic material and which will be substantially completely consumed when subjected to a temperature of at least 3000 and which have an average diameter of the order of 0.0015 millimeter, reducing such fibers to a length of from about 0.05 millimeter to about 0.075 millimeter, mixing said fibers in dry form with dry magnesium oxide powder in the approximate proportions of 5 ozs. of fiber to lbs. of magnesium oxide, then conveying the dry mixture into a briquetting machine and subjecting the mixture in dry form to a compacting pressure to produce pellets in dry form with the constituents coherent to a degree to withstand free handling, conveying and tumbling, [with a minimum of breakage.

3. A dry process of producing substantially pure magnesium oxide pellets which consists in mixing dry calcined magnesium oxide with fibers of an organic material of a character to be consumed without appreciable residue when subjected with the magnesium oxide toa temperature of about 3000 F., with the fibers and magnesium oxide powder in the approximate proportions respectively of 5 ozs. to -1001bs., the fibers being selected to have a length of not more than 0.075 millimeter, and of a diameter of the order of 0.0015 millimeter, maintaining the mixture in dry form and introducing the mixture in such dry form into a briquetting press, subjecting the dry mixture in the press toa pressure to produce pellets in which the constituents are coherent to a degree to withstand appreciable breakage upon handling, conveying and tumbling, introducing the dry pellets into a suitable kiln and subjecting the pellets to a firing temperature of about 3000 F. and thereby removing the fiber material from the pellets by burning and simultaneously effecting shrinkage of the pellet size and densification of the pellets to a high degree of hardness.

References Cited in the file of this patent UNITED STATES PATENTS 1,743,803 Arensberg et a1 Jan. 14, 1930 2,703,762 Slayter Mar. 8, 1955 2,957,752 Gloss Oct. 25, 1960 FOREIGN PATENTS 126,229 Great Britain May 18, 1919 

1. A COMPACT DRY MAGNESIUM OXIDE PELLET CONTAINING AS A BINDER APPROXIMATELY 3/1000 PERCENT OF RELATIVELY FINE CELLULOSIC FIBERS OF A LENGTH OF FROM ABOUT 0.05 TO 0.075 MILLIMETER AND OF A DIAMETER OF THE ORDER OF ABOUT 0.0015 MILLIMETER AND HAVING A SUFFICIENT HARDNESS TO RESIST CARCKING AND DECREPTIATION OF INTRODUCTION INTO AND PASSAGE THROUGH A SHAFT KILN.
 3. A DRY PROCESS OF PRODUCING SUBSTANTIALLY PURE MAGNESIUM OXIDE PELLETS WHICH CONSISTS IN MIXING DRY CALCINED MAGNESIUM OXIDE WITH FIBERS OF AN ORGANIC MATERIAL OF A CHARACTER TO BE CONSUMED WITHOUT APPRECIABLE RESIDUE WHEN SUBJECTED WITH THE MAGNESIUM OXIDE TO A TEMPERATURE OF ABOUT 3000* F., WITH THE FIBERS AND MAGNESIUM OXIDE POWDER IN THE APPROXIMATE PROPORTIONS RESPECTIVELY OF 5 OZS. TO 100 LBS., THE BEING SELECTED TO HAVE A LENGTH OF NOT MORE THAN 0.075 MILLIMETER, AND OF A DIAMETER OF THE ORDER OF 0.0015 MILLIMETER, MAINTAINING THE MIXTURE IN DRY FORM AND INTRODUCING THE MIXTURE IN SUCH DRY FORM INTO A BRIQUETTING PRESS, SUBJECTING THE DRY MIXTURE IN THE PRESS TO A PRESSURE TO PRODUCE PELLETS IN WHICH THE CONSTITUENTS ARE COHERENT TO A DEGREE TO WITHSTAND APPRECIABLE BREAKAGE UPON HANDLING, CONVEYING AND TUMBLING, INTRODUCING THE DRY PELLETS INTO A SUITABLE KILN AND SUBJECTING THE PELLETS TO A FIRING TEMPERA- 